If you're building an MCP server, sooner or later someone is going to ask: how does authentication work?

The MCP spec leaves this open. Most early servers shipped with no auth at all, or a hardcoded API key in an environment variable. That's fine for local Claude Desktop use. It falls apart the moment you publish a remote MCP server that real users connect to.

The right answer is OAuth 2.1 with PKCE, plus four RFCs that nobody enjoys reading: 9728 (Protected Resource Metadata), 8707 (Resource Indicators), 8414 (Authorization Server Metadata), and 7591 (Dynamic Client Registration). I know that sounds like a lot. Let me show you what it looks like in practice.

I'll use KavachOS, the auth library I built for AI agents. You don't have to use it.…